On Wed, Jan 26, 2011 at 4:50 PM, L. David Baron <dbaron@dbaron.org> wrote:
> On Wednesday 2011-01-26 11:50 +0100, Leif Arne Storset wrote:
>> I was asked recently whether and why 'object-fit: none' was removed
>> from the spec. Digging in the archives, it seems the proposal to
>> keep/revive it was forgotten amid other issues. So this is a request
>> to re-introduce 'none' as a value for 'object-fit'. The definition
>> would be "Render the content at its intrinsic dimensions,
>> overflowing if necessary."
>>
>> The use case is easy centering or positioning images without scaling
>> them. Centering images vertically in a box can be a PITA today,
>> especially if you don't know the dimensions. With image-fit:none, it
>> is super-easy. Have a look at the attached demo (only supported in
>> Opera 11, AFAIK).
>>
>> (To avoid any confusion: There were objections to our proposal of
>> another value, 'object-fit: auto', because the proposal was that
>> behavior depend on content type. These issues do not affect the
>> current proposal of 'object-fit: none', since no content-type
>> negotation takes place for 'object-fit: none'.)
>
> I think this is a bad idea. (I think the 'object-fit: scale-down'
> proposal later in the thread, however, is fine.)
>
>
> The main things I don't like about it derive from the fact that it
> causes replaced elements to overflow. I now see that
> object-fit:cover also does this, though I don't remember it doing
> that the last time I read the proposal. I'd really like to avoid
> getting into a situation where overflow applies to replaced
> elements; I'd prefer that they just never overflow their content
> box.
>
> (It's also quite inconsistent with what we ended up doing
> about the interaction of border-radius and replaced elements, since
> the border-radius is supposed to clip replaced elements. What
> happens with img { object-fit: cover; border-radius: 10px } ?)
>
> I think making it easy to overflow is generally a bad thing: layout
> systems should make it easy for authors to do what they want in ways
> that don't accidentally cause horrible layouts in a slightly
> different situation (e.g., slightly different viewport size, font
> size, etc.). Having an object-fitting mode that overflows by
> default fails this test (whereas 'scale-down' passes it). This is
> why I'd prefer that replaced elements not overflow their content
> box.
So, you support removing 'cover' and 'none' entirely? 'cover' is
indeed designed to overflow *by default*.
Another option is to simply disallow the overflow effect at all - that
is, *always* hide overflow on replaced elements, and ignore the
'overflow' property. That would solve your concern while still
allowing whatever use-cases 'cover' allows. (I'm not sure why 'cover'
is useful, personally.)
> Furthermore, I think we need to be solving vertical centering for
> all elements, not just replaced elements. We have some good
> proposals (including flexbox) on the table, and I hope they're
> implemented before 'object-fit' (which I think has substantially
> less demand than good layout systems) is. So I don't think we
> should design 'object-fit' to solve use cases that should already be
> solved by the time it's implemented.
I agree. If the only use-case for 'none' is centering an image,
that's not sufficiently useful to justify its existence.
> It's also unclear to me how much sense both 'none' and 'scale-down'
> make in a high-DPI world where CSS pixels mainly exist for
> backwards-compatibility.
Can you elaborate? I'm not sure I understand the objection here.
Raster images still map their pixels to CSS pixels, unless you've
specified otherwise in 'image-resolution'.
~TJ